What if Baby Has a Bad Reaction to a Vaccine?

If baby’s reacting to a vaccine, will I know it? What should I do?

About one in four babies has a reaction to a vaccine. Luckily, most aren’t serious — the most common reactions are redness, pain or tenderness at the injection site, mild fever and fussiness, says Cornelia Dekker, MD. These usually go away on their own within one to three days.

A minor reaction means the vaccine is doing its job — creating an immune response that will ultimately protect baby from infection, Dekker says. To ease pain, apply a cool wet cloth at the injection spot. If baby has a low fever, ask the pediatrician if it’s okay to give her medication, such as infant acetaminophen or ibuprofen.

Anything more serious or concerning, you should call the doctor immediately. This includes high fever (over 104 degrees) and signs of an allergic reaction such as facial swelling, hives or difficulty breathing. Chances of an allergic reaction are rare, Dekker says — about one in a million patients — and usually happen within hours of the vaccination.